1. Field of the Invention
This invention relates to the hot melt sizing of textile warp yarns, more specifically to a novel class of non-aqueous warp sizes and to a method of applying, removing, and disposing of them to eliminate the pollution problems commonly associated with conventional aqueous sizing methods.
2. Description of the Prior Art
The primary purpose of any textile warp size is of course to enhance the capacity for weaving or knitting of the yarn to which it is applied. Today's high-speed looms and knitting machines demand lubricity, flexibility, adherence to yarn, toughness, and other size characteristics for surpassing those of earlier machines. Faster moving loom parts which contact the yarns, such as shuttles and filling yarn projectiles, as well as the faster moving filling yarns which they carry through the warp yarns, or shed, likewise impose increasingly stricter requirements upon warp sizes.
Sizing of textile warp yarns, commonly called slashing, is thus an essential step in the preparation of yarns for weaving. Size is removed after weaving is complete. For many years the technology of warp sizing was dominated by the application of aqueous starch suspensions on massive machines known as slashers, the entire process being characterized from the beginning by high capital costs and large space requirements and more recently, in addition, by steadily rising energy costs and burgeoning water pollution problems. The advent of the more generally effective polyvinyl alcohol warp sizes did little to solve the application and removal problems associated with starch. These more modern aqueous sizes still utilized the slasher, they still required large outlays of energy to dry water from the yarn after slashing, and they merely substituted one kind of water pollution problem for another when the time came to remove the size after weaving. That is, the high B.O.D. (biological oxygen demand) of starch in waste desizing water was replaced as a pollution problem by the non-biodegradability of polyvinyl alcohol in the waste water, and hence a high C.O.D. (chemical oxygen demand). Elaborate systems have been devised to remove this polyvinyl alcohol, or in some instances to recover it for reuse, but these systems are expensive to install and operate. Also, the polymer they recover may be less pure than required for dependable reuse.
Despite its established position in the textile industry as the standard machine for application of size to warp yarns in preparation for weaving, the slasher has long been recognized to be a ponderous machine long overdue for replacement by something better. Particularly in today's atmosphere of urgent concern over conservation of energy and control of stream pollution, the slasher and the water-based sizes applied to yarns on it throughout the textile industry are coming under increasing scrutiny.
A number of systems have been proposed for solving the problems associated with applying aqueous warp sizes to yarns on the slasher. For example, U.S. Pat. No. 3,984,594, Sano et al, describes a process for sizing a cellulosic-fiber containing yarn with a non-aqueous solution of an acrylic or methacrylic copolymer in a halogenated hydrocarbon. The size is removed from the fabric after weaving by dissolution in the same or a different halogenated hydrocarbon solvent. This art process is thus complicated by the need to provide against air pollution by the toxic halogenated hydrocarbon. Enclosed drying facilities to remove solvent from the yarn prior to weaving are also required. Although typically urged as less expensive, particularly in energy terms, than drying of aqueous-sized yarns, drying of halogenated solvent from the sized yarn nevertheless remains as a significant equipment and process need and expense.
It is especially in the economic aspects of a sizing-desizing system based on expensive halogenated hydrocarbon solvents that the shortcomings of such a system become most prominent. The entire system is economically dependent upon keeping solvent losses and solvent makeup to an absolute minimum. This means not only that evaporative losses of solvent during the sizing and drying operations must be rigidly controlled, but that subsequent halogenated hydrocarbon desizing of fabric after weaving faces similar economic problems. A slasher type sizing machine is still employed.
For some years it has been recognized that a system for melt sizing of warp yarns would offer many advantages. At the sizing symposium of Sept. 9-12, 1974 in Budapest, Hungary (Melliand Textilberichte, English Edition, April, 1975, p. 262), it was observed, with respect to sizing machines and sizes: "All problems related with drying (energy costs, error sources) can be avoided, if sizing agents can be used which rigidify at room temperature. At present there is no satisfactory and practical solution; but it is probable that melt sizes will be important in the future."
U.S. Pat. No. 3,446,717, Kuroda, describes a method and apparatus for sizing warp yarns, wherein size is applied within a sizing chamber provided with a vat containing a quick solidifying molten size whose predominant composition is wax. Exemplified for application in the Kuroda apparatus is a molten size made with hardened castor oil, 2-ethylhexyl acrylate, and benzoyl peroxide, one of a number of sizes described in Japanese Patent Publication No. 14280/1965. More broadly, the latter publication describes certain classes of polymers or copolymers soluble in specified types of wax, capable of application to yarns by melt means. Desizing is not discussed.
U.S. Pat. No. Re. 29,287 describes another type of apparatus for applying molten size to yarn. This patent is particularly concerned with the demanding process of applying a melt size which can be removed by aqueous solvents. At present, however, the availability of such sizes is limited, and their costs high.
Another solution to the pollution problems associated with sizing of textile warp yarns which has been proposed in the art is to recover the size for reuse. Recovery for reuse is particularly attractive, at least in theory, because it offers greater opportunity for practical use of the more expensive types of sizes. Unfortunately, theory and fact usually part company in actual practice, either because recovery is not complete enough to be economically feasible, or because the recovered size carries down impurities with it which build up too much during repeated cycles of sizing and desizing.